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R.M. Conway, V. Sharma, K. Lai, M.J. Jager, M.C. Madigan; MUC18 (CD146/MelCAM/MCAM) Expression in Human Uveal Melanoma . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2224.
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MUC18 (CD146/MelCAM) is an important diagnostic marker of cutaneous melanoma, with increased expression in tumors associated with metastatic potential. MUC18 protein has been reported to be expressed in one uveal melanoma culture however, its expression in uveal melanomas and normal uveal melanocytes has not been studied in detail. In this study we investigated uveal melanoma cell lines, normal cultured choroidal melanocytes, and primary uveal melanomas for the expression of MUC18 mRNA and protein.
MUC18 expression (protein and mRNA) was assessed in uveal melanoma cell lines (OCM–1, –3, –8, OMM–1, 92–1 and Mel202) using immunoblotting and diagnostic RT–PCR. Sections of whole eyes with uveal melanomas of spindle and/or epithelioid morphology (n=18) were immunolabelled using a polyclonal antibody to the extracellular domain of MUC18 (R&D), and visualised using peroxidase and VectorRed (Vector Labs).
Immunoblotting of cell lysates from melanoma cell lines showed a positive band of ∼113kDa, and mRNA for MUC18 was also detected in all cell lines. In primary uveal melanoma, moderate to strong MUC18 immunolabeling of tumor cells was seen in 5/18 specimens (mixed spindle/epithelioid morphology, time from detection to enucleation <18 months). This immunolabeling was mostly cytoplasmic and patchy in distribution. Tumor vasculature, including vessel lumens, as well as networks/channels characteristic of more aggressive uveal melanoma, showed strong MUC18 immunoreactivity. MUC18 immunolabeling of extracellular matrix was also seen.
MUC18 was expressed in cultured uveal melanoma cells, but only in some primary uveal melanomas that were mostly of more aggressive histopathology. These observations taken together with immunolabling of tumor vasculature and in some cases, networks/channels, may suggest a role for MUC18 in tumor spread in some cases.
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